I know for some people reading more than one book is a big no no but for me I need a massive variety when reading.
For example at the minute i'm reading,
A Crown of swords - Robert Jordan
Possession - James Patterson
The Mortal instruments City of Bones - Cassandra Clare
Waiting To Be Heard - Amanda Knox
Cat and Mouse - James Patterson
The Exorcist - William Peter Blatty
For me it really depends what I'm doing and what mood i'm in. I tend to have a different book for a different activity such as, in the bath, reading in bed, reading on my phone when i have downtime in work, reading on the bus on the way to work.
I also find that a lot of the time I sit staring at my bookcase and just want to read them all!